Pascal Pointers Read Me

Pascal Pointers and Dynamic Variables Demonstration Package Dr. Jeffrey L. Popyack Assistant Professor Department of Mathematics and Computer Science Drexel University Philadelphia, PA 19104 (215) 895-2668 1. Introduction: This package is intended to provide users with a mechanism for learning to use pointers and dynamic variables in Pascal. The concept arose from the great deal of difficulty students have exhibited in learning this material in programming courses. This material is fundamental for further computer science work, yet often is not learned by students, partially because it is easier for the programmer to find an alternative way to implement his program than it is to learn the more elegant (and often more efficient) methods associated with dynamic variables. The package is designed as follows: The user is supplied with a display which shows an initial data structure. The display is similar to that used in most Pascal textbooks. The user is allowed to enter commands from a subset of Pascal commands which use pointer variables. As each command is entered, the display is updated to demonstrate the effect of the command on the given structure. Syntax and semantic errors are detected by the interpreter, with appropriate diagnostics. Some on-line help is also provided. A set of lessons is available, each of which provides some initial structure, and asks the user to alter the structure in some way. The user is not required to perform the lessons, however; this package is designed for use as a general tool which will correctly interpret and display any sequence of pointer-type commands. This package may therefore be used by an instructor for classroom demonstration. The instructor may also use the package to create additional lessons. The remainder of this report is organized as follows: Section 2 contains an explanation of pointers and dynamic variables in Pascal, and may be bypassed by the reader who is already familiar with this material. Section 3 contains instructions for using Pointer Demo and Section 4 shows a sample session. 1 2. About Pascal's Pointer Variables: Persons familiar with the concept of dynamic variables and pointers in Pascal may proceed to Section 3. Pascal allows the use of variable types that do not exist in some other languages, such as BASIC and FORTRAN. The user is also allowed to create new types for use in his program. One popular mechanism is the record structure, which allows a variable to have several components, each of which may have its own type. For instance, the declaration type StockHolder = record name : string[20] ; …